1. Field of the Invention
The present invention generally relates to an optical pick-up. More particularly, the present invention relates to an optical pick-up used in a MO (magneto-optic) drive or MO player.
2. Description of the Related Art
An optical pick-up comprising a laser diode, a variety of optical elements, an object lens, a photo detector and so on is incorporated in a MO-drive. The MO drive reads the information from a magneto-optic disc by using a laser, and writes the information to the magneto-optic disc both by using a laser and by applying a magnetic field.
In the optical pick-up, the optical power of a laser light emitted from the laser diode is monitored to control the intensity or the quantity of the laser light to be constant. FIGS. 3(a) and 3(b) illustrate conventional mechanisms for monitoring the intensity or the quantity of laser lights emitted from laser diodes 31, 41, respectively.
For example, in FIG. 3(a), a main laser beam for reading information from a magneto-optic disc or writing information to a magneto-optic disc is emitted in a direction A from a laser diode 31, while a sub laser beam for monitoring the laser power is emitted in a direction B from the laser diode 31. The direction B is opposite to the direction A. The sub laser beam is detected by a photo diode 32. The output signal from the photo diode 32 is inputted to an auto power control (APC) circuit. The APC circuit controls the current applied to the laser diode 31 based on the signal from the photo diode 32 to output a laser having the constant intensity and the constant quantity.
In FIG. 3(b), main laser beams for reading information from a magneto-optic disc or writing information to a magneto-optic disc is emitted in a direction C from laser diodes 41a, 41b and 41c respectively which are mounted on a three-beam laser diode array 41, while sub laser beams are emitted in the direction opposite to the direction of the main beams and detected by photo diodes 42a, 42b and 42c respectively. The output signals from the photo diodes 42a, 42b and 42c are inputted to an auto power control (APC) circuit. The APC circuit controls the each current applied to the each laser diode 41a, 41b and 41c based on the signals from the photo diodes 42a, 42b and 42c respectively to output lasers having the constant intensity and the constant quantity. The reference numeral 43 is a guide for guiding the sub beams emitted from the laser diodes 41a, 41b and 41c respectively to the respective photo diodes 42a, 42b and 42c.